Is Tegan returning?

Janet Fielding who played Tegan Jovanka from Logopolis in 1981 to Resurrection of the Daleks in 1984 tweeted this picture of herself with Peter Capaldi the 12th Doctor saying "Now what are we up to? Only Time will tell..."

DoctorWhoNews is reporting that the show will be filming in Lanzarote... aka "The Planet of Fire". Moffatt is quoted as saying the Doctor is returning to the site of a previous adventure, where things have 'taken a sinister turn'.